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Annual Meeting Optical Society of America

Two-color photo-associative ionization: observing intermediate steps of ultracold atomic collisions

Vanderlei Salvador Bagnato, Luís Gustavo Marcassa, Chia‐Wen Tsao, Yanping Wang, J. Weiner

Published Jan 1, 1993• 0 citations
Publisher

Abstract

Photo-associative ionization in sodium atoms has been the first two-body collision process investigated in optical traps.1
DOI
10.1364/oam.1993.tudd.5

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Collisions of ultracold trapped atoms ( T< 1mK) have opened a new field of atomic collisions with abundant opportunities for theory and experiments. Photo-associative ionization (PAI) in sodium atoms has been the first two-body collision Studied in optical traps3. In this process two ground state Na atoms absorb two photons during the course of the collisional encounter. The first absorption at long range put the colliding system on an attractive C3/R3 potential curve, and the two atoms begin to accelerate toward each other. A second absorption promotes the system to a doubly excited Na(3p)+Na(3p) potential curve from which the PAI process takes place at short range.

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Ultracold photo-associative ionization collisions of Na atoms in a magneto-optical trap: Optical block equation calculations

Y. B. Band, Paul S. Julienne, Carl J. Williams

We report new calculations of two-body associative ionization collisions between sodium atoms confined in a magneto-optic trap at ultracold temperatures. These collisions represent a new kind of {open_quotes}open{close_quotes} or dissipative collision for which the energy of the atom + applied light field need not be conserved due to spontaneous emission coupling to the vacuum modes of the radiation field and require density matrix methods rather than wavefunction methods to describe the collision. In these collisions the Na atoms must absorb a photon when they are in close enough proximity that a significant fraction of the excited population survives relaxation back to the ground state. The Na atoms accelerate towards each other on the excited molecular state and absorbs a second photon to a doubly excited state which then proceeds to associatively ionize at close range. Our calculations incorporate a molecular picture of the atomic collision, laser optical-field dressing of the molecular states participating in the dynamics, and population and coherence decay due to spontaneous emission. The effect of excited state hyperfine structure, which plays a critical role in the dynamics, is simulated by simplified models with a reduced number of states based on the full set of molecular-hyperfine adiabatic potentialmore » curves. Comparison is made with recent measurements of photo-associative ionization. rates as a function of optical field intensity from about 20 to 130 mW cm{sup -2}.« less

Bulletin of the American Physical Society•May 1, 1993•0 citations
Collisions of ultracold trapped atoms ( T< 1mK) have opened a new field of atomic collisions with abundant opportunities for theory and experiments. Photo-associative ionization (PAI) in sodium atoms has been the first two-body collision Studied in optical traps3. In this process two ground state Na atoms absorb two photons during the course of the collisional encounter. The first absorption at long range put the colliding system on an attractive C3/R3 potential curve, and the two atoms begin to accelerate toward each other. A second absorption promotes the system to a doubly excited Na(3p)+Na(3p) potential curve from which the PAI process takes place at short range.
We study photo-associative ionization (PAI) for sodium atoms held in a magneto-optical trap (T < 1 mK). The process is investigated using one and two laser frequencies. For a single color PAI, we measure the rate constant as a function of light intensity and the result is compared with calculation based on semiclassical Bloch equation theory. The measured rate constant appears to saturate sooner than theory. In the two-color PAI (TCPAI) we investigate individual steps of the process. Different combinations of laser frequencies prepare different populations in each of the hyperfine ground state and the contribution of each one in this collisional process is investigated. The comparison with theory allows a fairly clear understanding of PAI and TCPAI.
We report new calculations of two-body associative ionization collisions between sodium atoms confined in a magneto-optic trap at ultracold temperatures. These collisions represent a new kind of {open_quotes}open{close_quotes} or dissipative collision for which the energy of the atom + applied light field need not be conserved due to spontaneous emission coupling to the vacuum modes of the radiation field and require density matrix methods rather than wavefunction methods to describe the collision. In these collisions the Na atoms must absorb a photon when they are in close enough proximity that a significant fraction of the excited population survives relaxation back to the ground state. The Na atoms accelerate towards each other on the excited molecular state and absorbs a second photon to a doubly excited state which then proceeds to associatively ionize at close range. Our calculations incorporate a molecular picture of the atomic collision, laser optical-field dressing of the molecular states participating in the dynamics, and population and coherence decay due to spontaneous emission. The effect of excited state hyperfine structure, which plays a critical role in the dynamics, is simulated by simplified models with a reduced number of states based on the full set of molecular-hyperfine adiabatic potentialmore » curves. Comparison is made with recent measurements of photo-associative ionization. rates as a function of optical field intensity from about 20 to 130 mW cm{sup -2}.« less